U. S. FOREST SERVICE | RESEARCH PAPER | FPL | APRIL | 

FOREST PRODUCTS LABORATORY FOREST SERVICE 

U. S. DEPARTMENT OF AGRICULTURE MADISON. WIS 
Handsheets of various commercial and 

experimental papermaking pulps were 

ovendried in special drying frames that 

controlled the amount of shrinkage. Unstretched handsheets and those stretched 

predetermined amounts were dried with 

various allowances for shrinkage and 

tested in tension to determine the influence of restraint during drying on the 

strength, modulus of elasticity, and 

strain to failure. 

The results show that modulus of 

elasticity is independent of the type of 

pulp but increases with the degree of 

restraint during drying, and with the 

density of the handsheets. Modulus of 

elasticity in the direction of restraint 

was found to vary as the cube of density. 

Tensile strength and strain to failure, 

on the other hand, were dependent on 

the type of pulp, as well as on the degree 

of restraint and density of handsheets. 

Tensile strength increased with the degree of restraint and appeared to vary 

as a power function with density changes. 

Strain to failure decreased as degree 

of restraint increased; it increased, 

however, with increasing density. 

Handsheets ovendried under frame 

restraint exhibited different relationships of strength-to-density and 

modulus-to-density than handsheets of 

similar pulps pressed to different densities and air dried on polished disks in 

FPL 11 i 

the manner described in standard method 

T205 of the Technical Association of the 

Pulp and Paper Industry (TAPPI). For 

instance, the tensile modulus of elasticity of handsheets dried in frames 

varied as the cube of density while 

modulus of handsheets dried on polished 

disks varied as the square of density. 

Wet pressing was shown to increase 

the tensile elastic modulus by an amount 

much greater than could be accounted for 

by the reduction in thickness. Dry pressing, on the other hand, produced elastic 

modulus increases directly proportional 

to the decrease in thickness. The effect 

of frame restraint on tensile properties 

was dependent on the moisture content of 

the wet web before it was placed in the 

restraining frames. The higher the moisture content, the higher was the modulus of elasticity and tensile strength of 

the restrained handsheets. Changes in 

tensile properties as a result of restrained drying are retained to a substantial degree by the sheet, even after 

high humidity exposure or after being 

soaked in water for 60 hours andredried 

without restraint at 73° F. and 50 percent 

relative humidity. 

Stretching within limits before drying 

improved tensile strength and elastic 

modulus but reduced the strain to failure. 

The limits of stretching depended upon 

the type of pulp used. 
CONTENTS 

Page 

INTRODUCTION 

MATERIALS 

APPARATUS AND PROCEDURES 

PRESENTATION OF DATA 

DISCUSSION OF RESULTS

Preliminary Evaluation of the 

Effect of Wet Pressing

Effect of Restraint on the 

Modulus of Elasticity 

Tensile Strength-Density 

Relationships 

Effect of Restraint on 

the Strain at Failure 

Effect of Moisture Content 

at the Time of Restraint 

Permanence of Effects 

of Restraint 

LITERATURE CITED 

1 

2 

8 

11 

15 

21 

24 

25 

25 

ii FPL 11 
EFFECT OF RESTRAINT DURING DRYING 

ON THE TENSILE PROPERTIES OF HANDSHEETS 

BY 

Vance C. Setterholm, Forest Products Technologist 

and 

Warren A. Chilson, Chemical Engineer 

Forest Products Laboratory 1 Forest Service 

U. S. Department of Agriculture 

INTRODUCTION 

Adequate carton stiffness is one of the 

key factors in the production, merchandising, and sale of containers made from 

multi-ply cylinder board. Stiffness is important, not only to utilize the full 

strength of a container board, but to 

minimize carton bulge and permit successful operation of boxmaking equipment. The stiffness of multi-plycylinder 

board can be predicted if the modulus of 

elasticity of the separate component plies 

is known. Work at the Forest Products 

Laboratory has shown that the temperature and degree of restraint applied 

during the drying of the wet web will 

materially affect the strength and modulus of elasticity of the finished sheet (8).2 

Drying temperature and degree of 

restraint, however, are not the only important parameters influencing the mechanical properties of pulp handsheets. 

Pulping process and handsheet density 

were considered and found to be of basic 

importance in predicting the behavior of 

pulp handsheets under tensile stress. 

A large variety of pulps are available 

for the manufacture of multi-plycylinder board. The purpose of this project, 

undertaken with the cooperation of the 

Boxboard Research and Development 

Association at Kalamazoo, Mich., was to 

determine how restraining sheets prepared from beaten and unbeaten pulps 

during drying affected the tensile modulus of elasticity. These pulps were 15 of 

the most widely used, and were selected 

with the advice of the Stiffness Subcommittee of the Boxboard Research and 

Development Association. 

1

Maintained at Madison, Wis., in cooperation with the University of Wisconsin. 

2

Numbers in parentheses refer to “Literature Cited’’ at the end of the report. 
MATERIALS Freeness (Ml.) 

(1) Western softwood bleached kraft 700, 650, 530, 355 

(2) Western hemlock bleached sulfite 700, 600, 500, 280 

(3) Southern pine bleached kraft 420 

(4) Sweetgum bleached kraft The pulps and their Canadian Standard } (5) Aspen bleached cold soda 320 

freeness values after beating in the (6) Western softwood unbleached kraft 700, 620, 510, 330 

(7) Southern pine unbleached kraft 370 standard test beater are shown in the (8) Manila tabulating card stock 560 

(9) Waste newsprint following tabulation: (10) Corrugated boxes 520 

(11) Western hemlock unbleached sulfite 

(12) Spruce groundwood 50, 100 

(13) Milk carton stock 600 

(14) Eastern softwood bleached sulfite 

(15) Mixed hardwood semichemical pulp 450 

APPARATUS & PROCEDURES 

This study was designed to simulate 

some of the drying stresses induced in 

webs on the paper machine and to relate 

them to the resulting changes in strength 

and elasticity. Samples of pulp (360 

grams, ovendry basis) were beaten in 

the test beater to the freenesses indicated above. Handsheets weighing approximately 90 grams per square meter 

(air-dry basis) were formed on a 7-by 

9-inch sheet mold and wet pressed between blotters at 60 pounds per square 

inch for 5 minutes. Two opposite edges 

of the sheets were dried between heated 

platens for a distance of approximately 

five-eighths inch. 

These sheets were then clamped to a 

distance of one-half inch in the frames 

shown in figure 1, and the tension was 

adjusted either to provide various degrees of restraint or to stretch the sheet 

and then provide restraint. A flat supporting plate was placed under the sheet 

during clamping to provide support for 

the wet sheet. The drying frame and 

sheet were then placed on edge in an 

oven maintained at 150° F. for at least 

one-half hour (twice the time required 

to remove all free moisture). After drying, the sheets were conditioned at 73°F. 

and 50 percent relative humidity for at 

for at least 48 hours. The sheets were 

trimmed to 5 by 7-1/2 inches on a paper 

cutter and weighed on a triple-beam 

balance to the nearest 0.01 gram. 

Two tension specimens were cut from 

the center of each sheet. These were 

necked specimens, as shown in figure 2, 

and were cut from the sheet in the direction in which shrinkage stresses were 

induced by the applied restraint. Thickness measurements were made at the 

necked section to the nearest 0.0001 inch, 

with a dial-type micrometer (TAPPI 

Method T 411M-44). Tension tests of 

specimens were made on a test machine 

that used a mechanical drive and employed a load cell with an electrical 

resistance-type strain gage for measuring loads. 

2 FPL 11 
ZM 120 919 

Figure 1.--Frame used to hold wet handsheets 

when placed in drying oven. The degree of 

restraint is controlled by adjusting position 

of clamp attached to the crank. 

ZM 110 041 

Figure 2.--Paper tension specimen. 

The test machine was equipped with 

an autograph recorder for plotting load 

and testing machine crosshead movement 

simultaneously. Six specimens of each 

type of material were tested with a free 

length of about 5 inches between the grips. 

Loads were applied through a constant 

rate of head movement of 0.02 inch per 

mi nut e. Because of slippage and the 

irregular shape of the specimen, the 

crosshead movement was not used as a 

measure of strain. An optical, 

mechanical-type strain gage, described 

in Forest Products Laboratory Report 

No. 2066, was used to obtain accurate 

strain readings (9). Later a mechanicalelectrical strain gage was developed to 

obtain load-strain data (4). This directreading strain gage is shown in figure 3. 

Electrical output from the gage is fed 

into an amplifier and then directly to the 

autographic recorder of the testing machine. All tests were made in a room 

conditioned to 73° F. and 50 percent 

relative humidity. 

An additional investigation was made 

to determine the change in strength and 

elastic properties due to humidifying and 

soaking paper-machine webs previously 

dried under restraint. For this experiment, paper-machine webs of a western 

softwood bleached kraft pulp at a freeness of 370 milliliters were taken from 

the machine wire and ovendried at 150° F. 

unrestrained and with no allowance for 

shrinkage. These were then subjected to 

50, 65, 80, 90, and 97 percent relative 

humidity for 60 hours, as well as water 

soaking for 60 hours. All samples were 

then returned to a 50 percent relative 

humidity atmosphere for conditioning 

and tensile strength determinations. 

3 
ZM 123 455 

Figure. 3.--Straingage used to measure lengthwise specimen deformations under tensile load. 

Spring-loaded, knife-edged clamps (A) attach the gage firmly to the specimen. The weights 

(B) balance the system. The bearings (C, D, and E) allow the transformer core (G) to move 

in exact correspondence with the knife-edged clamps (A). The knife-edge bearings (D) are 

pinned to prevent lateral slippage, and springs are used to hold the knife edges in the grooves. 

This arrangement allows the lever arm to move freely, yet keeps the gage from flying apart 

when the specimen fails. The “cradles” (H) for the transformer (F) and core (G) can be 

moved laterally to provide the desired lever ratio. 

PRESENTATION OF DATA 

The effect of beating and restraint 

in frames during drying on 15 different 

commercial pulps is shown in table 1. 

This table shows the tensile strength, 

modulus of elasticity, and strain to failure for each pulp, as well as the pulp 

freeness, handsheet thickness, density, 

and conditions imposed during drying. 

Each of these values is an average of 

six determinations. 

Typical stress-strain curves for handsheets dried at different levels of restraint are shown in figure 4. 

The results of a study to determine 

the influence of density on tensile properties of air-dried handsheets of four 

different pulps are shown in table 2. 

Pulps used in the. preparation of these 

handsheets include: Western hemlock 

bleached sulfite beaten in the test beater 

to a Canadian Standard freeness of 305 

milliliters, corrugated board w a s t e 

beaten to a freeness of 510 milliliters, 

and unbleached western softwood kraft 

4 FPL 11 
beaten to a freeness of 450 milliliters and pressed for 5 minutes at several 

and to a freeness of 225 milliliters. different pressures in a screw press 

Handsheets were formed on a British with a capacity of 600 pounds per square 

sheet mold, placed on polished disks, inch. The handsheets were then air 

Table 1.--Tensile properties1 of handsheets from various pulps that 

were dried under varying degrees of restraint 

Canadian Drying Thickness Density Strength 

Standard conditions 2 

freeness 

WESTERN SOFTWOOD UNBLEACHED KRAFT 

700 

700 

700 

700 

620 

620 

620 

620 

620 

620 

510 

510 

510 

510 

330 

330 

330 

330 

700 

700 

700 

700 

650 

650 

650 

650 

650 

650 

530 

530 

530 

530 

355 

355 

355 

355 

U 

4 

2 

0 

U 

4 

2 

0 

S-2 

S-0 

U 

4 

2 

0 

U 

4 

2 

0 

U 

4 

2 

0 

U 

4 

2 

0 

S-2 

S-0 

U 

4 

2 

0 

U 

4 

2 

0 

7.5 2.26 1,850 

7.0 2.50 2,330 

6.5 2.56 2,490 

7.1 2.42 2,210 

7.2 2.44 2,240 

6.8 2.70 3,180 

6.0 2.72 2,650 

6.3 2.76 3,620 

7.3 2.64 3,870 

6.2 2.52 4,000 

6.9 2.69 3,390 

5.7 2.99 3,980 

5.9 3.02 5,300 

5.4 3.05 4,940 

7.2 2.76 4,360 

5.5 3.12 4,860 

5.6 3.18 5,300 

5.3 3.25 5,980 

BLEACHED WESTERN SOFTWOOD KRAFT 

7.6 2.28 990 

7.6 2.32 930 

7.6 2.37 1,070 

7.0 2.44 1,220 

6.6 2.67 1,930 

6.8 2.69 2,160 

7.1 2.55 2,190 

6.0 2.77 2,300 

7.2 2.43 2,730 

6.6 2.42 2,480 

7.0 2.77 2,630 

6.8 2.88 2,860 

5.4 2.98 3,410 

5.5 3.09 4,000 

6.2 2.82 2,440 

6.2 3.05 4,680 

5.0 3.24 5,140 

5.3 3.17 4,590 

700 

700 

700 

700 

600 

600 

600 

600 

600 

600 

500 

500 

500 

500 

280 

280 

280 

280 

WESTERN HEMLOCK BLEACHED SULFITE 

U 7.2 2.53 970 

4 6.4 2.63 1,070 

2 6.2 2.64 1,140 

0 6.5 2.66 1,350 

U 6.8 2.78 1,910 

4 5.5 2.96 2,110 

2 5.4 3.05 2,430 

0 5.6 3.13 2,820 

S-2 5.1 3.08 2,560 

S-0 5.8 3.07 3,080 

U 6.4 2.87 2,100 

4 5.0 3.13 2,730 

2 5.0 3.22 3,080 

0 4.9 3.21 3,580 

U 6.3 2.95 3,000 

4 5.2 3.58 3,670 

2 5.0 3.58 4.530 

0 4.7 3.69 4,890 

Modulus of Strain 

failure 

1,000 

p.s.i. 

139 

204 

295 

425 

178 

318 

358 

534 

513 

592 

199 

384 

583 

640 

186 

508 

596 

931 

100 

183 

229 

230 

159 

269 

314 

521 

457 

494 

176 

336 

495 

660 

143 

527 

582 

642 

130 

160 

205 

305 

182 

314 

468 

588 

490 

619 

187 

349 

457 

587 

231 

514 

738 

851 

4.62 

4.26 

3.34 

1.66 

4.80 

4.60 

3.13 

1.90 

2.06 

1.25 

7.20 

4.70 

3.90 

2.25 

7.50 

5.60 

3.50 

2.10 

3.53 

2.22 

1.67 

1.10 

4.31 

4.04 

2.96 

1.64 

1.46 

.a4 

5.89 

4.08 

3.10 

1.92 

6.58 

5.12 

4.00 

2.44 

3.10 

2.85 

1.90 

.98 

4.88 

3.89 

1.63 

1.40 

1.38 

1.00 

5.20 

4.92 

3.22 

1.67 

7.30 

4.70 

3.04 

1.86 

Canadian Drying 2 Thickness Density Strength Modulus of Standard conditions elasticity 

freeness 

Ml. 

430 

430 

430 

430 

430 

430 

170 

170 

170 

170 

170 

170 

520 

520 

520 

520 

520 

520 

560 

560 

560 

560 

560 

560 

370 

370 

370 

370 

370 

370 

420 

420 

420 

420 

420 

420 

320 

320 

320 

320 

320 

320 

600 

600 

600 

600 

600 

600 

U 

4 

2 

0 

S-2 

S-0 

U 

4 

0 

2 

S-2 

S-0 

U 

4 

2 

0 

S-2 

S-0 

U 

4 

2 

0 

S-2 

S-0 

U 

4 

0 

S-2 

S-0 

U 

4 

2 

0 

S-2 

S-0 

U 

4 

0 

S-2 

S-0 

U 

4 

2 

0 

S-2 

S-0 

SWEETGUM BLEACHED KRAFT 

6.6 2.90 2,770 

5.6 3.17 3,520

5.6 3.20 3,890 

5.1 3.24 4,610

5.4 3.17 4,650 

5.6 3.02 4,680 

WASTE NEWSPRINT 

2.08 1,220 

2.11 1,140 

2.09 1,000 

8.4 

8.2 

8.4 

8.2 2.01 1,010

8.2 2.02 1,050 

8.2 2.05 1,250

CORRUGATED BOARD WASTE 

7.9 2.35 1,900

7.3 2.36 2,410

7.5 2.40 2,620

6.7 

7.6 2.34 2,760

7.9 2.27 2,890 

TABULATING CARD WASTE 

7.9 2.62 2,230

6.6 2.60 2,200 

6.7 

7.4 

6.8 

6.9 

2.51 2,960 

2.61 2,240 

2.78 2,800 

2.63 2,600 

2.53 2,580 

SOUTHERN PINE UNBLEACHED KRAFT 

7.1 2.56 3,400 

6.4 3.10 4,730 

6.1 3.11 4,910 

5.5 3.17 5,800 

5.3 3.08 5,640 

5.7 2.90 5,430 

SOUTHERN PINE BLEACHED KRAFT 

6.5 2.86 4,210 

5.1 3.35 4,860 

5.0 3.48 5,670 

4.8 3.44 5,690 

5.5 3.46 5,310 

5.3 3.30 5,290 

COLE SODA PULP 

8.8 2.02 1,190 

8.2 2.07 1,250 

8.4 2.10 1,240 

2.18 1,750 

8.5 2.09 1,590 

8.9 2.02 1,630 

8.2 

MILK CARTON STOCK 

7.16 2.64 2,241 

6.72 2.67 2,150 

6.25 2.73 2,390 

6.17 2.72 3,060

6.63 2.62 2,630 

6.48 2.52 2,780

1,000 

p.s.i. 

247 

437 

567 

656 

661 

733 

1.37 

146 

147 

156 

160 

235 

165 

224 

317 

402 

395 

433 

232 

213 

263 

403 

346 

417 

147 

390 

479 

620 

582 

636 

250 

470 

674 

711 

705 

659 

109 

141 

173 

236 

228 

243 

l70 

198 

250 

351 

302 

371 

Strain 

to 

failure 

Pct. 

7.38 

5.74 

3.05 

2.25 

2.31 

1.67 

2.14 

2.37 

1.90 

1.39 

1.28 

.85 

5.02 

4.21 

3.95 

3.26 

2.04 

2.01 

1.12 

8.18 

5.82 

3.80 

2.53 

2.46 

1.64 

8.90 

6.24 

4.10 

3.18 

2.58 

1.91 

3.33 

2.42 

1.68 

1.24 

1.16 

1.06 

5.23 

4.46 

3.91 

2.80 

2.12 

1.39 

Ml. Mils Lb. per 

1,000 

sq. ft. 

per mil 

P.s.i. Pct. Mils Lb. per 

1,000 

sq. ft. 

per mil 

P.s.i. 

2 

2 

4.73 

2.85 

1.81 

1.65 

1.02 

5 
Table 1.--Tensile properties1 of handsheets from varoius pulps that 

were dried under varying degrees of restraint--Con. 

Canadian 

Standard 

freeness 

M1. 

Drying 2 Thickness Density Strength Modulus of Strain 

conditions elasticity to 

failure 

Mils Lb. per 

1,000 

sq. ft. 

per mil 

P.s.i. 1,000 

p.s.i. 

Pct. 

BLEACHED EASTERN SOFTWOOD SULFITE 

380 U 5.5 3.13 3,010 184 6.73 

380 4 5.2 3.41 3,100 246 5.92 

380 2 4.7 3.53 353 3.58 

380 0 4.7 3.53 3,690 426 2.34 

380 S-2 3.63 3,920 446 2.11 

380 S-0 4.6 3.47 4,510 506 1.61 

UNBLEACHED WESTERN HEMLOCK SULFITE 

350 U 6.4 2.99 2,820 172 6.70 

350 4 5.2 3.47 3,740 349 5.40 

350 2 5.0 3.52 3,870 412 3.67 

350 0 4.9 3.65 4.770 532 2.42 

350 S-2 5.0 3.67 568 2.11 

350 S-0 5.0 3.60 5,750 658 1.59 

UNBLEACHED SPRUCE GROUNDWOOD 

50 U 8.1 2.23 1,550 139 3.06 

50 4 8.1 2.21 1,630 147 2.94 

50 2 8.0 2.24 1,850 194 2.10 

50 0 8.1 2.24 1,840 198 1.69 

50 S-2 8.0 2.17 1,920 219 1.59 

50 S-0 8.1 2.16 1,960 230 1.29 

100 U 9.4 1.94 1,020 108 1.96 

100 4 8.9 2.05 1.110 112 2.28 

100 2 8.9 1.94 121 2.07 

100 0 8.7 1.96 1,270 160 1.43 

100 S-2 9.1 2.02 1,180 149 1.44 

100 S-0 9.0 2.00 1,220 152 1.23 

MIXED HARDWOOD BLEACHED NEUTRAL SULFITE SEMICHEMICAL 

450 U 5.8 3.16 4,450 341 3.86 

450 4 5.6 3.38 3,950 351 4.00 

450 2 5.4 3.60 4,500 442 3.22 

450 0 5.2 3.71 632 1.96 

1Results are average of 6 tests made after conditioning at 75° F. and 50 percent relative humidity. 

dried unrestrained 

4--Sample dried with a 4 percent allowance for shrinkage. 

2--Sample dried with a 2 percent allowance for shrinkage. 

0--Sample dried with no allowance for shrinkage. 

2U--Sample 

S-2--Samplestretch 3 percent and dried with a 2 percent allowance for shrinkage. 

S-0--Sample stretch 3 percent and dried with no allowance for shrinkage. 

dried on the disks in a conditioned 

atmosphere of 73° ± 3-1/2° F. and 

50 ± 2 percent relative humidity. Tests 

were made at these standard conditions 

to determine the tensile strength, modulus of elasticity, and strain to failure. 

Table 3 shows the influence of restraint and stretch on tensile properties 

when handsheets were partially dried before frame restraint was applied, and the 

effect of applying restraint and releasing 

the restraint before drying was comZM 

Figure 4. T ypical stress-strain curves for 

handsheet of southern pine kraft pulp (370-

milliliter Canadian Standard freeness). 

pleted. This work was done on 7- by 

9-inch handsheets from a bleached western softwood kraft pulp beaten in the 

test beater to a freeness of 650 milliliters. Restraint was applied using the 

drying frame shown in figure 1. 

A somewhat related investigation was 

made to determine how tensile properties were affected when paper-machine 

webs were dried to higher and higher 

solids content before restraint was applied. These tests were made on 7-by 

9-inchwet webs of a southern pine kraft 

pulp processed in a beater to a freeness 

of 450 milliliters. 

Results of an additional experiment to 

determine the permanence of tensile 

strength, modulus of elasticity, and 

6 FPL 11 
Table 2.--Effect of density on tensile properties1 of handsheets 

from four pulps wet pressed to different densities 

Basis weight Pressure 

1,000 

P.s.i. 

Density Tensile Modulus of Strain 

strength elasticity to 

failure 

Lb. per 

sq. ft. 

Lb. per 

1,000 

sq. ft. 

per mil 

P.s.i. 1,000 

p.s.i. 

Pct. 

Table 3.--Effect of moisture content at the time restraint 

was applied on tensile properties1 

drying 

Unrestrained. . . . . . . . 

4 pct. shrinkage 

allowance. . . . . . . . . 

2 pct. shrinkage 

allowance. . . . . . . . . 

No shrinkage 

allowance. . . . . . . . . 

Stretch 3 pct., then 

unrestrained. . . . . . 

Stretch 3 pct., then 

2 pct. shrinkage.. 

Stretch 3 pct., no 

shrinkage ......... 

Dried to 50 pct. 

moisture content, 

then fully 

restrained. . . . . . . . 

Dried to 50 pct. 

moisture content 

under restraint, 

then dried 

unrestrained. . . . . . 

Dried to 30 pct. 

moisture content 

under full 

restraint, then 

dried 

unrestrained. . . . . . 

6.6 

6.8 

7.1 

6.0 

6.8 

1.2 

6.6 

6.3 

6.9 

7.6 

Lb. per 

1,000 

2.67 

2.69 

2.55 

2.77 

2.45 

2.43 

2.42 

2.73 

2.56 

2.55 

Tensile Modulus of Stretch 

strength elasticity 

1,920 

2,160 

2,190 

2,300 

1,760 

2,720 

2,480 

2,320 

1,840 

2,000 

160 

269 

314 

523 

183 

455 

495 

380 

209 

260 

4.31 

4.04 

2.96 

1.64 

3.36 

1.46 

.84 

1.91 

3.27 

3.51 

1

Average of 6 tests. Specimens conditioned and tested at 75° F. and 50 percent relative humidity. 

Table 4.--Effect of humidity and water soaking on strength 

and elastic properties1 of restraint-dried webs 

Unrestrained 50 pct. 

Thickness 

Density Tensile Modulus of Strain to 

strength elasticity failure 

Machine Cross- Machine Cross- machine Crossdirec- machine direc- machine direc- machine 

tion direc- tion direc- tion direc- tion tion tion 

Mils Lb. per P.s.i. P.s.i. 1,000 1,000 Pct. Pct. 

p.s.i. p.s.i. 

per mil 

10.4 2.34 2,750 1,600 145 70 6.9 8.7 

Restrained . . .do. . . 8.1 2.57 4,180 3,190 560 380 2.1 2.4 

Do. . . . . . . 65 pct. 2.52 3,900 2,710 450 365 2.7 2.3 

Do. . . . . . . 80 pct. 8.2 2.54 4,080 2,720 300 3.0 2.8 

Do. . . . . . . 90 pct. 8.4 2.49 4,100 2,650 460 280 3.3 3.1 

Do. . . . . . . 97 pct. 8.6 2.45 4,150 3,060 450 300 3.7 3.1 

Do. . . . . . . water 8.9 2.37 1,600 2,390 270 140 

soak 

1Averago of 6 tests. Specimens conditioned and tested at 75° F. and 50 percent rel- ative humidity after exposure shown in column 2. 

Conditions for Thickness 

Density 

Mils P.s.i. 1,000 

p.s.i. 

Pct. 

Condition Exposure 

relative 

humidity 

1,000 

sq. ft. 

3.31 

3.32 

3.03 

3.02 

3.01 

3.09 

2.95 

2.98 

3.02 

3.29 

2.78 

2.82 

3.09 

2.57 

2.47 

2.72 

2.64 

2.55 

2.60 

2.63 

4.32 

3.50 

3.25 

3.42 

3.19 

3.16 

3.41 

3.24 

3.47 

2.94 

2.78 

3.31 

3.30 

2.98 

3.31 

3.03 

3.37 

2.96 

3.02 

3.02 

15.0 

15.2 

14.8 

14.0 

13.6 

13.6 

13.4 

15.3 

15.2 

15.3 

13.8 

14.0 

13.8 

13.8 

14.0 

13.8 

13.9 

14.2 

14.2 

14.1 

13.9 

13.9 

13.6 

13.2 

14.2 

13.9 

13.6 

13.8 

14.3 

14.0 

13.5 

13.7 

13.0 

13.2 

12.9 

12.7 

1Results are 

WESTERN HEMLOCK BLEACHED SULFITE: 305 FREENESS 

12.0 3.65 6,190 687 

14.5 3.74 6,400 677 

21.8 3.86 6.120 696 

28.2 3.88 792 

41.0 3.89 6,220 726 

60.0 4.04 6,480 720 

115.0 4.26 7,710 770 

211.0 4.50 7,710 766 

315.0 4.52 7,940 862 

440.0 4.62 8,450 868 

CORRUGATED BOARD WASTE: 510 FREENESS 

12.0 2.28 2,513 276 

14.5 2.35 2,893 302 

21.8 2.37 2,666 285 

28.2 2.45 2,846 295 

41.0 2.54 2,930 289 

60.0 2.68 3,160 331 

115.0 2.83 3,590 398 

211.0 2.90 3,800 416 

315.0 3.00 4,180 446 

440.0 3.10 4,310 499 

WESTERN SOFTWOOD UNBLEACHED KRAFT: 450 FREENESS 

10.25 2.59 3,800 320 

20.5 3.00 4,680 408 

41.0 3.27 5,660 505 

61.5 3.49 6,270 562 

62.0 3.65 6,270 630 

123.0 3.69 6,610 666 

164.0 3.81 6,350 604 

246.0 3.97 7,130 671 

328.0 4.12 7,390 685 

410.0 7,710 813 

513.0 4.09 7,260 766 

615.0 4.21 7,930 728 

WESTERN SOFTWOOD UNBLEACHED KRAFT: 225 FREENESS 

9.8 3.65 9,670 671 

13.7 3.81 780 

19.6 3.85 8,920 691 

29.3 3.94 9.930 733 

77.8 4.22 836 

127.0 4.33 11,030 a15 

254.0 4.40 10,890 

391.0 11,620 1,016 

585.0 4.65 11,290 917 

average of 4 tests made after conditioning at 75° F. and 

50 percent relative humidity. 

strain to failure are given in table 4. 

Here handsheets, which had been dried 

under restraint in two directions, were 

subsequently humidified or immersed in 

water for 60 hours and then redried unrestrained at 73° F. and 50 percent 

relative humidity. 
DISCUSSION OF RESULTS 

Preliminary Evaluations of 

the Effect of Wet Pressing 

The tensile properties of paper are, to 

a substantial degree, dependent on paper 

density. The manipulation of paper 

density is easily accomplished at any of 

the several stages of paper manufacturing, particularly by variation in wet-web 

pressure. Highly beaten pulps require 

less pressure than lightly beaten pulps 

to achieve the same density. On the 

other hand, handsheets from lightly 

beaten pulps are capable of greater variations in density with the same amount 

of wet pressure. Horio and Onogi (3) 

show that density variation can have a 

large effect on modulus of elasticity. In 

fact, they conclude that the modulus of 

elasticity varies as the square of density. 

These findings, with regard to density 

and modulus, are corroborated by Luner, 

Karna, and Donofrio (5), who also showed 

that modulus varies as the square of 

density. Further, they found that the 

bonded area of handsheets was a function 

of modulus of elasticity. 

In this report, which is aimed chiefly 

at measuring the effects of restraint 

during drying on the strength and elastic properties of paper, it seemed necessary to take into consideration the 

differences in pulp that might be attributable to density, as well as to the effects of restraint. The problem was to 

find what the intrinsic effects of restraint during drying were on the 

strength and elastic properties of papermaking pulps. If sheetmaking and pressing conditions are held constant, a meas8 FPL 11 
ZM 125 523 

Figure 5. --Relationship between tensile strength 

and density of handsheets wet pressed to different densities and dried while in contact 

with polished plates. 

ure could be obtained of the practical 

effects of restraint during drying on the 

strength and elastic properties of handsheets. 

A preliminary study to measure the 

effect of density was made with four 

pulps: (1) Unbleached softwood kraft at 

a 450-milliliter Canadian Standard freeness, (2) unbleached softwood kraft at a 

225-milliliter freeness, (3) bleached 

softwood sulfite at a 305-milliliterfreeness, and (4) waste corrugated box pulp 

at a 510-milliliter freeness. In general, 

handsheets were prepared according to 

TAPPI standard procedures, except that 

the pressures applied during the pressing operation were varied over a range 

of 0 to 600 pounds per square inch to 

produce sheets with a wide range of densities. Densities varied from 2.3 to 4.7 

pounds per 1,000 square feet per mil, or 

0.444 to 0.906 gram per cubic centimeter. 

Since these handsheets were dried on 

disks, allowing very little shrinkage, 

they were considered to be fully restrained in all directions during drying. 

The results of this study are presented 

in table 2 and illustrated in figures 5 and 

6. These data show that neither the tensile strength nor the elastic modulus can 

be said to vary directly in proportion to 

density. The relationship between 

strength and density (fig. 5) shows that 

tensile strength increases as a power 

function with density increase. Tensile 

strength for these handsheets was dependent on the type of pulp, as well as 

the degree of beating as shown by lines 

drawn through the plotted points having 

the same slope. 

The relationship between the tensile 

modulus of elasticity and density (fig. 6), 

shows that modulus of elasticity varies 

as the square of density and is independent of pulp type, as well as thedegree of 

beating. Based on the data obtained, the 

elastic modulus of handsheets wet 

pressed to any density and dried on polished disks can be predicted from the 

density value. The increase in elastic 

modulus with density is attributed to an 

9 
ZM 125 524 

Figure 6.--Effectof handsheet density on modulus 

of elasticity for handsheets wet pressed to 

different densities and dried while in contact 

with polished plates. 

increased area of fiber bonds. Whether 

the increase in elastic modulus can also 

be attributed to shorter segments 

between fiber bonds is a matter for 

speculation. Undoubtedly, both occur. It 

seems evident that the increase is not 

due to a change in the microcreping at 

fiber bonds, since the restraint applied 

was constant. 

Wet pressing is emphasized here in 

contrast to dry pressing or calendering 

which is not likely to result in the formation of additional fiber bonding. Experience has shown that dry pressing or 

calendering will increase modulus of 

elasticity only in proportion to the reduction in thickness caused bythe pressing operations. If, on the other hand, an 

appreciable amount of moisture (beyond 

fiber saturation) is present at the time 

of pressing, the modulus of elasticity of 

the paper will be increased beyond that 

which can be attributed to the reduction 

in thickness. 

An illustration of the effect of dry 

pressing versus wet pressing on the 

elastic modulus of paper or handsheets 

is shown in figure 7. Data showingthe 

effect of wet pressing on the elastic 

modulus-to-density ratio were taken 

from table 2. Those illustrating the effect of dry pressing on the modulus-todensity ratio were taken from compression tests on 10-, and 12-mil filter 

paper. In this instance, the 12-mil filter 

paper was reduced to thicknesses of 8 

and 10 mils by passing the dry paper 

through the calender stack of the experimental paper machine. These data, 

though somewhat limited and different in 

origin, clearly show that the specific 

elastic modulus is not improved by dry 

pressing and, further, that wet pressing 

will increase the modulus of elasticity 

beyond that which can be attributed to 

reduction in sheet thickness. 

Effect of Restraint on the 

Modulus of Elasticity 

When wet handsheets are restrained 

from shrinking in a rigid drying frame, 

the development of drying stresses 

resulting from surface tension and bond 

formation imposes a stress on the sheet 

in the direction of the applied restraint. 

10 FPL 11 
Figure 7.--Relationshipbetween density and modulus of elasticity divided by density for wet-pressed 

handsheets and dry-pressed papers. 

In theory, this results in an improvement in the stress distribution (7), as 

well as a reduction in the amount of 

microcreping at the bondsites (6). The 

application of restraint results in an increase in tensile strength of failing load, 

an increase in elastic modulus, and a 

decrease in strain to failure. There is a 

small increase in density, which is probably caused by an increase in bonding. 

This increase in density increases with 

decreased shrinkage allowance and de11 
creases with stretching. The following 

tabulation is a composite of density data 

in table 1:

Condition of 

restraint 

Unrestrained 

percent shrinkage 

2 percent shrinkage 

Restrained 

1 percent stretch 

percent stretch 

This is another 

Average density 

of all handsheets 

(lb. per 1,000 sq. ft. 

per mil) 

2.62 

2.82 

2.87 

2.92 

2.74 

2.66 

indication that the 

increase in density can be accounted for 

by an increase in the area of the fiber 

bonds. The decrease in density with 

stretching would be expected to reduce 

the modulus of elasticity. Therefore, the 

increase in elastic modulus with stretching must be due to other factors, such 

as improved stress distribution and prevention of microcreping at fiber bondsites. 

The data in table 2 showing the 

relationship between modulus of elasticity and density for handsheets pressed 

to different densities and dried on disks, 

are based on different pulps at several 

different freenesses. Therefore, it is 

assumed from the general grouping about 

a single line that the effect of density on 

modulus of elasticity is independent of 

pulp type and freeness level. 

Data in table 1 for unbleached western 

softwood kraft, bleached western hemlock sulfite, and bleached western softwood kraft show that the .modulus of elas12 

ticity of fully restrained handsheets 

dried in frames more nearly varies as 

the cube of density than as the square of 

density. Handsheets air-dried on disks 

do not show this relationship. Sheets of 

similar density ovendried and restrained 

by drying frames are stiffer than similar 

sheets air-dried on disks. The difficulty 

in concluding that disk drying versus 

“frame drying” is basically different results from the fact that there are other 

variables such as temperature to which 

these differences might be attributed. 

If handsheet data from three pulps of 

the same type are examined, there is 

support for the view that ovendried 

frame-restrained sheets are stifferthan 

sheets of the same density that were airdried on disks. These data are shown in 

table 5. 

Table 5.--Comparisons of modulus of elasticity obtained 

by two methods of restraining sheets 

Pulp Restrain- Canadian Density Modulus of 

ing Standard elasticity 

method freeness 

Difference 

Ml. Lb. per 

1,000 

sq. ft. 

per mil 

P.s.i. Pct. 

Western hemlock Frame 280 3.69 851,000 

bleached sulfite Disk 305 3.65 687,000 24 

Waste corrugated Frame 510 2.51 402,000 39 board Disk 520 2.54 289,000 

Unbleached western Frame 510 3.05 640,000 

softwood kraft Disk 450 3.00 408,000 57 

A further examination of the possibility 

that elastic modulus varied as the cube 

of density was made using all the data 

available in table 1. This examination 

confirmed the supposition, and more 

interestingly, it showed that the degree 

of restraint during drying was also of 

basic importance. The relationships are 

shown in figures 8, 9, 10, 11, and 12. 

These graphs show that a straight line 

passing through the origin will fit most 

of the points on these curves. Some scatter exists on all of the curves above 

FPL 11 
ZM 125 535 

Figure 8.--Effect of density on modulus of 

elasticity when handsheets from different 

pulps are dried in unrestrained condition. 

ZM 125 537 

Figure 9.--Effect of density on the modulus of 

elasticity when handsheets from different 

pulps are dried with a 4 percent allowance 

for shrinkage. 

ZM 125 533 

Figure 10.--Effectof density on the modulus of 

elasticity when handsheets from different 

pulps are dried with a 2 percent allowance 

for shrinkage. 

density-cubed values of 37. Most of this 

scatter is introduced by plotting the data 

for the eastern bleached and the western 

unbleached sulfite pulps. Whether the 

handsheets from these pulps are typical 

or whether this marks the endpoint of 

the density-modulus relationship is not 

certain. More research should be conducted to explore the limit and precision 

of this relationship. 

Curves 8 to 12 are reproduced in composite form in figure 13. This family of 

curves shows clearly the large effect 

drying under restraint has on the elastic modulus. As an example, the following tabulation of values was prepared for 

13 
-- 

handsheets with a density of 3 pounds per 

1,000 square feet per mil. These data are 

graphically illustrated in bar chart form 

in figure 14. 

Wet-web treatment Increase in 

before drying elastic modulus 

(Pct.) 

Unrestrained 

Allow 4 percent shrinkage 38 

Allow 2 percent shrinkage 66 

Restrained 106 

3 percent stretch 212 

125 521 

Figure 11.--Effect of density on the modulus of 

elasticity when handsheets from different 

pulps are dried with no allowance for shrinkage. 

ZM 125 521 

Figure 12.--Effect of density on modulus of 

elasticity when handsheets from different 

pulps are stretched 3 percent and not allowed 

to shrink while drying. 

More important, the evidence shows that 

the relationship between modulus of elasticity and density is not greatly affected 

by the amount of beating or kind of pulp 

used in the preparation of handsheets. 

The modulus of elasticity or stiffness of 

the handsheets in this study appears to 

depend primarily on the density of the 

handsheet and degree of restraint that 

is applied during the drying of the wet 

web. 

The fact that elastic modulus varies as 

the cube of density, rather than the 

square as other researchers have found, 

is attributed to the drying temperature 

and the differences in drying in a frame 

14 FPL 11 
ZM 125 520 

Figure 13.--Compositegraph showing effect of 

density on modulus of elasticity for different 

pulps dried under several conditions of reas opposed to drying on a polished disk. 

Undoubtedly this is the source of some 

of the difficulties that arise in relating 

data obtained from handsheets made 

according to TAPPI procedures with data 

obtained from machine-made paper. 

Tensile Strength-Density 

Relationships 

The relationship between tensile 

strength and density for pulps included in 

table 1 is shown in figure 15. Strengthdensity data show four distinct classification groups as follows: (Group 1) unbleached softwood kraft pulps; (group 2) 

bleached softwood kraft pulps; (group 3) 

bleached and unbleached softwood sulfite, 

as well as bleached hardwood semichemical pulps; and (group 4) hardwood cold 

soda, waste news, waste corrugated, and 

unbleached spruce groundwood pulps. In 

order to obtain these curves, data for unrestrained handsheets and those that had 

been stretched 3 percent were omitted. 

Data for unrestrained pulp s were 

omitted, because accurate thickness 

straint. 

ZM 125 526 

Figure 14.--Effect of restraint during drying on modulus of elasticity at constant density of 

3 pounds per 1,000 square feet per mil. 
ZM 125 542 

Figure 15.--Effect of density on tensile strength for handsheets from different pulps dried with 

no allowance for shrinkage, as well as 2 and 4 percent allowance for shrinkage. 

measurements could not be made on the The scatter of data makes it difficult 

more or less cockledunrestrainedhand- to bring out any distinct differences besheets. Data for handsheets that had been tween the levels of restraint. The four 

stretched 3 percent prior to drying were groupings of data about single curves 

treated separately . appear to be fairly logical. For example, 

16 FPL 11 
the data show that at any given density, 

unbleached softwood kraft has the highest 

tensile strength. 

The data do show that tensile strength 

is primarily dependent on the pulping and 

bleaching process and on the density 

achieved in manufacture of the handsheets. At the same density, tensile 

strength is independent of freeness. The 

principal effect of beating on tensile 

strength is to alter pulp density. This 

view was also expressed by R. H. 

Doughty in 1932 (1). One of the basic 

differences between this study and 

Doughty’s work was the method of drying 

the handsheets. After pressingwet sheets 

to a desired density, Doughty dried them 

between blotters in a vacuum oven, using 

the blotters to keep the sheets flat. Since 

no mention was made of the sheets sticking to the blotters, it is assumed that 

the blotters offered little restraint to the 

normal shrinking tendencies of his handsheets. The present study shows, as did 

Doughty, that the most important effect 

of changing the freeness by beating was 

to alter the sheet density. 

A plot on log scale of tensile strength 

versus density of handsheets pressed and 

air-dried to different densities shows a 

series of straight lines with the same 

slope (fig. 16). If these data are combined 

with data for the 15 pulps shown in 

figure 16, in which handsheets were ovendried in frames, there are two curve 

families, each with a distinct and 

separate slope. The important differences between these two groups arc 

drying temperatures and the manner in 

which restraint was applied. In one case, 

restraint was applied in only one direction in ovendrying with frames, and in 

the other restraint was applied from all 

directions in the flatwise plane of the 

sheet- when the webs were air-dried on 

flat plates. This, in part at least, explains why it is difficult to relate standard handsheet strength values to those 

obtained on samples made on the paper 

machine. 

The tensile strength-density relationships were studied for unrestrained 

handsheets to further explore differences 

in drying conditions. It is fairly certain 

that thickness measurements on unrestrained handsheets are usually too high 

because of the wrinkles in the sheets. 

However, the density and thickness values of sheets with a 4 percent shrinkage 

allowance very nearly approximate the 

true values for unrestrained handsheets. 

Strength values were accordingly adjusted for more realistic thicknesses 

and the strengths plotted against the adjusted densities. The curves in figure 17 

show exactly the same slope as those of 

the sheets that were restrained in 

frames. It therefore appears that the difference between the slope of the curves 

for plate-dried sheets and those for 

sheets dried in frames is not due to the 

fact that restraint is applied in one direction only because the lack of restraint 

does not change the slope. It does indicate, however, that drying temperature 

is a primary factor in the strength-todensity relationships. 

The effect of stretching wet webs 

3 percent and then restraining them is 

shown in figure 18. Results of stretching 

wet webs 3 percent followed by 2 percent relaxation are shown in figure 19. 

These curves, along with figures 15 and 

17 were used to prepare figures 20 to 23, 

which are strength-densitycurves showr

-

ing the effect of restraint on the tensile 

17 
ZM 125 543 

Figure 16.--Relationshipbetween tensile strength and density for handsheets dried under restraint 

in drying frames and sheets pressed to different densities and dried on polished disks. 

18 FPL 11 
ZM 125 544 

Figure 17.--Showing effect of density on tensile strength for handsheets from different pulps 

dried in unrestrained condition. 

strength of the four groups of pulps. 

As previously shown, increasing the 

amount of restraint during drying will 

result in subsequent increases in density 

of the dried sheet. While these changes 

are not large, they are fairly consistent. 

Density increases and then decreases 

along a scale of decreasing shrinkage 

allowance and beyond to one of stretching and restraining the wet sheet. While 

tensile strength normally (under constant restraint) would be expected to increase and decrease with density 

changes, applying restraint increases the 

tensile strength above that which can be 

accounted for by changes in density. In 

fact, tensile strength may even increase 

while density decreases. It is easy to 

attribute these effects of drying restraint 

to improvements in the stress distribution but, while reduction of the microcreping may improve the elastic modulus, it is difficult to visualize how it will 

benefit tensile strength. 

One of the most interesting aspects 

of the influence of restraint during dry-
125 530 

Figure 18.--Effect of density on tensile strength for handsheets from different pulps that have 

been stretched 3 percent and then dried with no allowance for shrinkage. 

ing on tensile strength is the way in which 

the different pulp groups respond to variations in the restraint and stretching 

during drying. The kraft pulps (bleached 

or unbleached, figs. 20 and 21) are more 

influenced by restraint than are the 

sulfite pulps. This is illustrated by 

greater spread between the 3 percent 

stretch and unrestrained handsheet 

tensile values. These differences probably reflect basic differences in the ability of the sulfite and kraft pulps to form 

fiber-to-fiber bonds or intrinsic differences in fiber properties. Similarly, 

bleaching reduces the ability of kraft 

pulps to benefit in tensile strength from 

the effects of drying under restraint. 

Reworked pulps (fig. 23) such as newsprint or pulps containing a high percentage of groundwood benefit in tensile 

strength by drying under restraint but 

not to as great a degree as chemical 

pulps. 

The increase in tensile strength at a 

constant density (3 pounds per 1,000 

square feet per mil), which results from 

frame restraining during drying 

stretched and unstretched handsheets of 

pulp groups 1, 2, and 3, is shown in 

figure 24. This composite figure illus20 FPL 11 
ZM 125 528 

Figure 19--Showingeffect of density on tensile strength of handsheets from different pulps that 

have been stretched 3 percent and allowed to shrink 2 percent in length during drying. 

trates that the type of pulp is an important factor in improving tensile 

strength. 

Effect of Restraint on the 

Strain at Failure 

Much has been said in this report about 

the improvements in tensile strength and 

elastic modulus that are achieved as a 

consequence of drying handsheets under 

restraint. In addition, there are noticeable improvements in dimensional stability (2) that result from restrained 

drying. These benefits, however, are obtained at the expense of stretch or toughness of the dried paper. While the loss 

in strain to failure is immediately evident 

by examining table 1, the graphical presentation in figures 25 through 28 shows 

additional comparisons. The figures 

show strain at failure versus density 

curves at different levels of restraint 

for the same pulp grouping that was obtained in the analysis of strength and 

density data. For these curves the density values shown for unrestrained handsheets were those obtained on handsheets 

where the shrinkage allowance was 

4 percent. 

21 
ZM 125 534 

Figure 20.--Composite graph for handsheets 

from pulps in group 1 showing effect of 

density on tensile strength at all levels of 

restraint during drying. 

ZM 125 532 

Figure 21.--Composite graph for handsheets from 

pulps in group 2 showing effect of density on 

tensile strength at all levels of restraint 

during drying. 

ZM 125 525 

Figure 22.--Composite graph for handsheets 

from pulps in group 3 showing effect of 

density on tensile strength at all levels of 

restraint during drying. 

ZM 125 522 

Figure 23.--Compositegraph for handsheets from 

pulps in group 4 showing effect of density on 

tensile strength at all levels of restraint 

during drying. 
ZM 125 529 

Figure 24.--Effect of restraint during drying on 

tensile strength at constant density of 3 pounds 

per 1,000 square feet per mil. 

ZM 125 540 

Figure 26.--Effectof density on tensile strain to 

failure for handsheets from pulps in group 2 

at five levels of restraint or stretching. 

For most of the pulps, the over all 

percent reduction in strain to failure 

from the unrestrained to fully restrained 

condition was about 70 percent. Stretching the wet webs 3 percent resulted in an 

additional loss of stretch of about percent. At any given density, the unbleached 

kraft pulps (fig. 25) showed greater 

stretch than the bleached kraft pulps 

(fig. 26). The bleached kraft pulps, in 

turn, showed greater stretch than the 

sulfite pulps (fig. 26). ZM125 541 

Figure 25.--Effect of density on tensile strain to For unrestrained sheets, the stretch 

failure for handsheets from pulps in group 1 is controlled by the degree of beating. 

at five levels of restraint of stretching. As greater restraint is applied during 

23 
drying, the influence of processing becomes less. Thus, in a general way, 

stretch is influenced more by restraint 

than it is by refining in the test beater. 

However, the more beating and the higher 

the density of handsheets, the greater 

will be the effect of restraint on stretch. 

Effect of Moisture Content 

at the Time of Restraint 

Results show that, within the moisture 

limits of the experiment (20 to 60 percent), the higher the moisture content at 

the time the restraining is accomplished, 

the higher the strength and modulus of 

elasticity of the dried sheet. This point 

is illustrated in figure 29. 

Figure 27.--Effect of density on tensile strain to 

failure for handsheets from pulps in group 3 

at five Bevels of restraint or stretching. 

ZM 125 536 

Figure 28.--Effectof density on tensile strain to 

failure for handsheets from pulps in group 4 

at five levels of restraint or stretching. 

ZM 125 538 

Figure 29. Tensile properties of paper as 

affected by moisture content at time of 

restraint. 

24 FPL 11 

ZM 125 539 
Permanence of Effects are not seriously reduced by a subseof Restraint quent high-humidity exposure (table 4). 

Although water soaking reduced the elasData obtained in this additional tic modulus greatly, neither the elastic 

experiment show that much of the im- modulus nor the strength curve returned 

provement in strength and elastic mod- to the original unrestrained levels. 

ulus induced by drying under restraint 

LITERATURE CITED 

(1) Doughty, Randall H. 

1931, 1932. The relationship of 

sheet properties and fiber properties in paper. Paper Trade Jour. 

93(2):39-44; 93(15):44-49; 95(9): 

29-34. 

(2) Fahey, D. J., and Chilson, W. A. 

1963. Mechanical treatments for 

improving dimensional stability of 

paper. Tappi 46(7):393-399. 

(3) Horio, M., and Onogi, S. 

1951. Dynamic measurements of 

physical properties of pulp and 

paper by audiofrequency sound. 

Jour. Applied Phys. 22(7): 971-977. 

(4) Jewett, Douglas M. 

1963. An electrical strain gage 

for the tensile testing of paper. 

U.S. Forest Service Research Note 

FPL-03. Forest Products Laboratory, Madison, Wis. 

(5) Luner, P., Karna, A. E. U., and 

Donofrio, C. P. 1961. Studies 

in interfiber bonding of paper; the 

use of optically bonded areas with 

high yield pulps . Tappi 44(6) : 40 9-

414. 

(6) Page, D. H., and Tydeman, P. A. 

1961. A new theory of shrinkage, 

structure, and properties of paper. 

in formation and structure of 

paper, Vol. 1. Trans., British 

Paper and Board Makers’ Assn. 

Symposium . Oxford. 

(7) Schultz, John H. 

1961. The effect of straining during drying on the mechanical and 

viscoelastic behavior of paper. 

Tappi 44(10):736-744. 

(8) Setterholm, Vance C., Chilson, 

Warren A., and Luey, A. T. 1962. 

Effect of temperature and restraint 

during drying on the tensile properties of handsheets. U.S. Forest 

Prod. Lab. Rpt. 2265. 

(9) Setterholm, Vance C., and Kuenzi, 

Edward W. 1956. Method for 

determining tensile properties of 

paper. U.S. Forest Prod. Lab. 

Rpt. 2066. 

25 
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